Internal combustion engine



FIG. 1 is a front perspective view of an internal combustion engine showing my design;

FIG. 2 is a perspective view of the rear thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a top plan view thereof;

FIG. 6 is a bottom plan view thereof;

FIG. 7 is a side view thereof; and,

FIG. 8 is an opposite side view thereof. 

The ornamental design for an internal combustion engine, as shown and described. 